1. Field of the Invention
The present invention relates to waveguides, and more specifically to optical waveguide interconnectors.
2. Description of the Related Art
Communications and computing systems based on electronic interconnection schemes have nearly reached their limits of any further improvement, while demands for higher bandwidth and speed are ever increasing for military and civilian applications. This scenario has led researchers to seriously consider new computing architectures based on optoelectronic interconnects. Employment of optical technologies is already a reality in the area of comrnunications. However, full commercial realization of optical computation and communications networks depends on the successful transmission and control of high-speed signals among processing elements, memories and other peripherals with minimal losses. In fact, by now, several key components and manufacturing technologies needed for this technological revolution have attained an appreciable state of maturity. A large variety of optoelectronic devices such as lasers, optical amplifiers, electro-optic switches, modulators, and detectors exhibit excellent performance characteristics. Also, the transmission characteristics achieved for optical waveguides and fibers allow optical transmission spans from intra-wafer interconnection to global optical communications.
The compatibility and reliability aspects of optoelectronic packaging are the major hurdles to taking full advantage of novel achievements in optoelectronic device technology. The difficulty in packaging mismatched discrete optoelectronic components generally results in high coupling losses. The mismatch is mainly a consequence of spatial and angular variations of individual optoelectronic components and separations of array devices. These components, which are often fabricated on different substrates, have different mode sizes, numerical apertures and component separations. For example, laser diodes can be made on GaAs, detectors made on silicon, and modulators made on LiNbO3. The dimensions of these discrete devices are pre-selected to optimize their performance, and vary from a few microns (single-mode waveguides and vertical cavity surface-emitting lasers) to hundreds of microns (photodetectors and multi-mode plastic fibers). The requirements of individual element performance optimization make system integration very difficult with comfortable alignment tolerance, and consequently integration results in high packaging costs. In many scenarios, the packaging cost is approximately 50% of the total system cost. Achieving efficient optical coupling among various devices with sufficient alignment tolerance is particularly difficult when using prisms, gratings, or optical lenses.
Two-dimensional (2-D) tapered waveguides have been employed to improve optical coupling among various optoelectronic devices. Coupling efficiency can be further improved if three-dimensional (3-D) tapered waveguides can be fabricated and employed. However, none of the existing optoelectronics or microelectronics fabrication methods available to optoelectronics industrial sectors is suitable for making satisfactory 3-D tapered waveguide devices, varying from a few microns to hundreds of microns in both horizontal and vertical directions. To grow a high-index waveguide layer hundreds of microns in thickness is impractical using any existing waveguide fabrication method used for inorganic materials such as GaAs, LiNbO3 and glass. The 3-D compression molded polymeric waveguide described herein is a solution to bridge the huge dynamic range of different optoelectronic device-depths varying from a few microns to hundreds of microns.
The ends of the waveguide are designed to provide interfaces with fiber-optic cables. There are three problems that have occurred at the ends, or interfaces, of the waveguide:
(1) inconveniently high coupling loss due to the optical mode mismatch,
(2) strict alignment tolerance which makes the packaged system vulnerable to harsh environments, and
(3) separation mismatch when array devices (such as laser diode arrays, smart pixel arrays, photodetector arrays and optical fiber/waveguide arrays) are employed.
Due to the planarized nature of these devices mentioned above, the most common approach based on microlenses is bulky and very expensive because it requires complicated three-dimensional spatial and angular alignments.
Conventional optoelectronic packaging technologies have failed to provide low-loss coupling among various optoelectronic devices, including laser diodes, optical modulators, waveguide splinters, single-mode optic fibers, multi-mode optic fibers and optical detectors. The above mentioned three problems are solved by the present invention.
The present invention discloses an apparatus and method for interconnecting electro-optical devices with differing optical mode profiles. The present invention is a three-dimensional tapered waveguide with a specified index of refraction that adiabatically transmits the fundamental mode of the photo-optic signal from an electro-optical device at the waveguide""s input end to a different electro-optical device at the waveguide""s output end. The input and output ends of the three-dimensional tapered waveguide are configured to match the optical mode profiles of the electro-optical devices that the waveguide interconnects.
The three-dimensional tapered waveguide can be configured in an array, to interconnect arrays of electro-optical devices with differing optical mode profiles and inter-device separation. Depending upon system packaging requirements, the waveguide can be manufactured on a substrate for interconnecting devices mounted on or near substrates such as printed circuit boards or silicon substrates, or encased in a plug-type arrangement for interconnecting electro-optical devices such as fiberoptic cables. The substrate or encasing material has a different index of refraction than the waveguide material.
Additionally, the present invention comprises a compression-molding technique for fabricating 3-D tapered polymeric waveguides. This embodiment of the present invention comprises a two-piece molding tool that includes a substrate and a mold plunger where the mold plunger provides a cavity having the shape of the desired 3-D-tapered waveguides. The present invention provides an appropriate amount of molding material that is spin-coated or laminated onto the substrate. The film thickness is equal to the maximum thickness of the tapered structure. The molding process begins with the heating of the mold plunger and the polymer film. Then the two parts of the mold are brought together under pressure that causes the polymer film, which is softened by heat, to be compression molded into the shape of the stamp of the desired 3-D-tapered waveguides.